The invention relates to a mirror arrangement for reflex cameras having the features of the preamble of claim 1.
For the purpose of visually viewing the recording object in a reflex camera, the light coming from the objective is projected onto a matte focusing screen via a main mirror, which is pivotably mounted in the camera housing. Through a partially transmissive zone in the main mirror, a second detail image of the recording object is formed in an intermediate image plane of an autofocus device or a light metering arrangement usually arranged in the bottom of the camera housing via a secondary mirror that is pivotably mounted on the main mirror. The autofocus device here indicates in a known manner the sharpness state of the recording object in the form of a deviation of the intermediate image plane from a desired position.
For the purpose of recording an image, the main mirror is pivoted upward out of the imaging beam path and the secondary mirror that is rotatably mounted on the main mirror is placed against the main mirror. In order to avoid stray light from the eyepiece region, the secondary mirror here covers the partially transmissive zone in the main mirror.
A permanently exact position of the secondary mirror as part of the autofocus device is a necessary prerequisite since very small deviations of the intermediate image plane from the desired position must be identified for very precise automatic focusing.
For the purpose of viewing the recording object, the main mirror is placed generally at 45° with respect to the optical axis of the objective in the beam path to the image plane, with the distances from the matte focusing screen and from the image plane being equal. The dimension of the surface area of the main mirror is matched to the image field to be recorded. The installation space for the main mirror must in this case be dimensioned such that, while the main mirror is pivoted in and out of the imaging beam path, its front edge does not collide with the lens that is last in the direction of light or the mount of the objective placed into the camera.
The distance of the light exit surface of the last lens from the image plane is referred to as back-vertex focal length. For objectives with a short focal length, short back-vertex focal lengths are advantageous for improving the optical power. The aim is therefore to shorten the installation space for the main mirror without having to limit its surface area for the image transfer to the matte focusing screen.
It is known to perform the pivoting movement of a flap not about a spindle which is fixed to the housing but to connect to the connecting rod of a four-bar mechanism. The front edge of the flap in this case performs a movement path that is flattened with respect to a circular path and permits the shortening of the installation space for the flap. If such a connected movement is selected for the main mirror and the secondary mirror is pivotably mounted on the main mirror, the point of articulation of the secondary mirror, during the adjustment of the pivoted-in end position of the main mirror, performs, due to the connected movement of the main mirror, a movement which results in misalignment of the secondary mirror. This is not the case in the case of single mounting of the main mirror in a fixed pivot joint because the secondary mirror moves practically exclusively in the mirror plane during the adjustment of the main mirror. This is true in particular when the two mirrors are located at an angle of about 90° relative to each other. In addition, only two rotational points with play negatively affect the exact position of the secondary mirror in contrast to four-bar mechanisms.
A mirror arrangement for an electronic reflex camera is known from EP 1 612 600 A1. The camera includes an optical and an electronic viewfinder system. The partially transmissive main mirror is mounted pivotably on a lever which itself is mounted rotatably in the camera housing.
For the purpose of recording an image, the lever is pivoted into a position parallel to the matte focusing screen and the main mirror is pivoted into a position that is aligned with the lever. Additional stops must be pivoted-in in order to avoid entry of stray light from the eyepiece region.
In order to view the recording object via the optical viewfinder system, the lever is rotated into an inclined position and the main mirror is orientated at 45° with respect to the optical axis of the objective. Arranged downstream of the partially transmissive main mirror is a driven secondary mirror, which is mounted separately in the lower camera housing and guides part of the imaging beam bundle onto an autofocus detector.
In order to observe the recording object via the electronic viewfinder system, the secondary mirror is pivoted into a neutral position outside the autofocus beam path and the main mirror on the lever is pivoted into a position which corresponds to the position of the secondary mirror in the case of optical viewfinding. The imaging beams passing through the main mirror are incident on a CCD image sensor and the imaging beams reflected on the main mirror are incident on the autofocus detector. The mechanical complexity for mounting and for driving the two mirror systems independently from one another is very great.